Process for fireproofing cellulosic materials



Patented May 29, 1934 UNITED STATES PROCESS FOB FIBEPEOOFING CELLULOSIC MATERIALS Martin Leatherman, Hyattsville, Md., dedicated to the free use of the Public in the territory of the United States of America No Drawing. Application January 5, 1934, Serial No. 705,403

2Claims.

(Cl. ill-68) (Granted under the act of March '3, 1883, as amended April 30, 1928; 370 0. G. 757) This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928 and the invention herein described, if patented, may be manufactured and used by or 5 for the Government for governmental purposes without the payment to me of any royalty thereon.

I hereby dedicate the invention herein described to the free use of the public in the territory of the United States of America to take effect upon the granting of a patent to me. This invention relates to an improvement in the fire-proofing of cellulosic materials which also lessens deterioration of cellulose fabrics by sunlight and weather, and is an improvement on an invention made by me, patent application for which was filed under Serial No. 652,032 on January 16, 1933.

It is well established that hydrated stannic oxide prevents flaming of cellulosic materials when properly placed therein. The prior art has involved impregnating the fabric or other cellulose material with a solution of sodium stannate of suitable concentration and then immersing the impregnated material in a solution of ammonium sulfate whereby a metathetical reaction results in the deposition of hydrated stannic oxide in the cellulose fibre and the formation of sodium sulfate and free ammonia. All soluble products of the reaction are washed out of the fibers so that the only purpose served by the ammonium sulfate is the liberation of the stannic oxide. However, the presence of ammonia causes the stannic oxide to be deposited under alkaline conditions, which are undesirable.

As disclosed in my previous application referred toabove, I have discovered that the flameproofing efliciency of the stannic oxide can be greatly increased by certain changes in the meth- 0d of precipitation. If, instead of an ammonium salt, I use a. salt of a strong acid with a weakly base forming metal, the hydroxide of which is water insoluble, I achieve better results for two reasons. In the first place, the insoluble hydroxide has no undesirable alkaline reaction with the result that less alkali is adsorbed and absorbed by the stannic oxide. In the second place the insoluble metal hydroxide is deposited in the cellulose fibers with the stannic oxide. I have discovered that many hydrated metal oxides, other than stannic oxide, such as manganese dioxide, cupric oxide and ferric oxide, have very marked flame-proofing properties either alone 5 or in connection with stannic oxide; so that the presence of any or of several of these metallic oxides in the fabric is of great value. Furthermore, some of these metallic oxides have pigmenting properties which are desirable for reasons that will be explained below.

I might achieve the precipitation of stannic oxide reasonably free of alkali by using a dilute acid solution, asolution of ammonium salt acidifled with added acid or by use of a solution of an acid salt such as sodium bisulphate. However, for reasons as stated I prefer to precipitate the hydrated stannic oxide by interaction of the sodium stannate, previously dried within the cellulose material, with solutions of any one of various metallic salts or of mixtures of these salts. The chief requirements are that the metallic salts be suiiiciently hydrolyzed in aqueous solution to yield a solution of decidedly acid reaction, and that the hydroxide of the metal be insoluble. The acidic nature of these salt solutions serves to precipitate the stannic oxide from the sodium stannate freer from adsorbed alkali, while at the same time the basic nature of the sodium stannate solution serves to precipitate the hydrated oxides of any of the metals present in the salt solutions. In many cases the hydrolytic effect can be further assisted by adding additional acid to the salt solution, care being taken not to add enough acid to redissolve the precipitated oxides. As examples of metallic salts which may be used I will mention alums containing chromium or iron and mixtures of such alums, ferric and chromium salts other than alums, salts of copper, titanium, nickel, cadmium, zinc, aluminum, thorium, cerium, vanadium, lanthanum, zirconium, stannlc and stannous tin, etc. There are obviously other salts which may be used, but these suflice to indicate the method. I have found it desirable to mix certain salts for various reasons. Ordinarily the total salt content of the precipitating salt solution will not exceed 20% by weight.

As an example a '7 to 10% aqueous solution of thorium and cerium nitrates in the proportion to give a ratio of 99 parts of thorium oxide and 1 part cerium oxide when precipitated may be used. 100

Also there may be used a 20% aqueous solution of crystallized ferric sulphate.

Orthere may be used a 5 to 10% aqueous acidified solution of a vanadyl salt, the acid used to acidify being that corresponding to the salt used.

I may or may not find it advantageous to use acid in the salt solutions utilized, dependent on the degree of alkalinity of the sodium stannate, since it is desirable to neutralize the alkali in the sodium stannate because the presence of alkali mum concentration of sodium hydroxide to which may be added any desired excess of alkali, but I do not wish to be restricted in any way by this definition. It is obvious that thesodium can be replaced by any of the other alkali metals such as potassium. The dried fabric is immersed for a short time in the desired metallic salt solution whereby a mutual precipitation is effected. The alkali in the sodium stannate is neutralized by the acid radical of the metallicsalt by the mechanism of base exchange. Simultaneously, hy-

drated stannic oxide and the hydroxide of the metal in the salt are deposited in the cellulose material.

Since metallic oxides prevent propagation of flame by or in cellulose materials but do not prevent vigorous flameless combustion or after-glow, it is necessary to supplement the action of the metallic oxides with some other material to prevent fiameless combustion. It has been found that certain types of chlorinated organic compounds are excellent for this purpose. Chlorinated vinyl resins have been used and 'I'have discovered that chlorinated rubber is likewise graph. 1 I

It is known that stannic oxide is capable of causing marked deterioration of cellulose materays.

rial under the influence of certain light rays. It has likewise been observed that the various chlorinated organic materials used for glow-proofing the cellulose also cause rapid deterioration of cellulose under the effect of certain kinds of light organic substances canbe very greatly lessened by use of a pigmenting or coloring material other than white on the cellulose fiber. It has not been clearly established as to the processes taking place during the said deterioration, but it is evi= dent that these processes are, if not initiated, at

' the fibers. It may be assumed that the pigmenting material either absorbs the activating light rays or otherwise prevents their action.. I may.

use as the pigmenting material colored metallic hydrated oxides such as those of iron, chromium, copper, cobalt, nickel, manganese, etc., mutually precipitated with stannic oxide as already shown, or. I may prefer to use an additional pigment placed in or on the cellulose material as the final step in the treating process either by impregnation by precipitation in the cellulose material or placed and held thereon by means of a binding material which may or may not be alsoa wateras dry as possible. further, is then subjected to the fireprooflng ngencies described above. satisfactory. There are, no doubt, other suitable" materials. However, these substances' are allob 'g jectionable for the reason stated in the next para--- I have discovered that the deteriorating effect of stannic oxide and that of the chlorinated proofing'agent, or which may be the glow-proofing resinous material itself. Asexamples I may use earthy pigments such as raw or burnt umber, raw or burnt sienna, ochchrome green, chrome yellow, Prussian blue, metallic aluminum,

etc. I may also use organic dyes where they are' found to-have a protective action. In practice the pigment may be impregnated into or depos ited upon the cellulose material either before or after the chlorinated material has been deposited.

thereon. The glow-prooflng'material may also serve as the binding agent. A pigment may be applied with a binding agent after all other treat ments have been completed.

It will usually be desired to, fire-proof un bleached cotton fabrics directly. These fabrics,

are very resistant to saturation or impregnation even by an alkaline solution. I have found it advisable to first treat these water-resistant fabrics as follows: Oneper cent by weight or there-' abouts of an agent, such as the true sulphonate types represented by the type formula R-SO3X carbon chain of twelve or more carbon atoms and X is hydrogen or a metallic element, is added to water and the fabric is immersed in the solution until the fabric is thoroughly impregnated or saturated. The assisting agent is then rinsed out o! the fabric with water and the fabric is squeezed Thefabric, without drying 'my'invention: I

1. The process of fire-proofing and preserving cellulosic materials and fabrics which comprises immersing the fabric until thoroughly saturated Y Having fully disclosed my discovery 1' claim as dried cellulosic material in a water solution of a salt of a strong mineral acid with a weakly baseforming metal, the hydroxide of which is water-' insoluble, then washing the material in water to remove acid residues, drying the material, impregnating the material with chlorinated rubberand incorporating in the resulting cellulose fabrics coloring materials- 2.'The process of fire-proofing and preserving cellulose materials and fabrics which comprises immersing the fabric until thoroughly saturated I in a one per cent solution of a metallic salt of .a sulfate ester of an aliphatic alcohol, rinsing the cellulosic material thoroughly in water, pressing out as much of the .wateras possible; then im'- pregnating thecellulosicmaterial with sodium stannate, drying, and then immersing the dried, cellulosic material in an aqueous solution of ferric sulphate, then washmg the cellulosicmaterial in water toremove acid residues, drying the, cellulosic material and impregnating it with chlorinated rubber.

, MARTIN LEATHERMAN. 

